FIELD OF THE INVENTION
The present invention relates to the art of controlling the emissions of acid gas, particularly sulphur oxides (SO.sub.2 and SO.sub.3) from flue gases produced in a coal fired boiler. Sulphur oxides are formed when coal containing sulphur is burned in a furnace. The combustion process results in the production of hot flue gas which contains unacceptable levels of SO.sub.2 and/or SO.sub.3. These sulphur oxides are generally eliminated or reduced to acceptable levels by scrubbing the gas with particulate scrubbing materials such as limestone granules. Typically, the flue gas containing sulphur oxide is scrubbed by passing the flue gas through a bed of wet limestone which reacts with the sulphur oxide contained in the flue gas to produce a solid reaction product (calcium sulphate and calcium sulphite). The production of a solid reaction product containing sulphur effectively removes the gaseous sulphur compounds from the flue gas.
The solid reaction product forms a crust around the limestone particles which must be periodically removed because the presence of the crust produces a surface blinding effect which interferes with the reaction between the scrubbing particles and the sulphur oxides. Thus, the particles containing a crust of reaction product are periodically regenerated by removing the crust so as to expose a fresh surface of scrubbing material for reaction with the sulphur oxides.
The present invention relates to an improvement in the configuration of a moving bed of wet scrubbing material which permits the scrubbing to proceed in a highly effective and efficient manner.